The sex steroid testosterone regulates reproductive behaviors such as intra-male fighting and mating in non-humans. Correlational studies have linked testosterone with aggression and disorders associated with poor impulse control, but the neuropsychological processes at work are poorly understood. Building on a dual-process framework, we propose a mechanism underlying testosterone’s behavioral effects in humans: reducing cognitive reflection. In the largest behavioral testosterone administration study to date, 243 men received either testosterone or placebo and took the Cognitive Reflection Test (CRT), that estimated their capacity to override incorrect intuitive judgments with deliberate correct responses. Testosterone administration reduced CRT scores. The effect was robust to controlling for age, mood, math skills, treatment expectancy and 14 other hormones, and held for each of the CRT questions in isolation. Our findings suggest a mechanism underlying testosterone’s diverse effects on humans’ judgments and decision-making, and provide novel, clear and testable predictions.
The circulating testosterone levels of healthy men decline with advancing age. This process is characterized by considerable inter-individual variability, the causes of which are of significant biological and clinical interest but remain poorly understood. Since sleep quantity and quality decrease with age, and experimentally-induced sleep loss in young adults results in hormonal changes similar to those that occur spontaneously in the course of aging, this study examined whether some of the variability in circulating testosterone levels of older men can be related to objective differences in their sleep.
We observed the response of serum growth hormone (GH) and testosterone (T) to a progressive resistance strength training program. Basal levels (after a 12-h fast) of GH and T were measured in young (23 years) and elderly (63 years) subjects before and after a 12-week training program. The response of GH and T to an acute bout of exercise was also measured. The exercise training, which involved all the major muscle groups, was conducted on Nautilus equipment and required 45-60 min for completion. The subjects completed three sets of lifts with 8-10 Reps/set. Blood was drawn from an anticubital vein, centrifuged (1169 g) for 15 min and the serum frozen for later analysis. The acute exercise blood samples were taken immediately before and after the exercise and at 15 min post-exercise during week 1 and 12. The hormone assay was carried out with radioimmunoassay kits for GH and T. The basal level of GH increased by % in the young and by only 3% in the elderly but neither change was significant. In response to a single exercise session GH levels in the young went from +/- to +/- ng/ml before training and from +/- to +/- after training. Each response was significant (P less than ) as were the pre-post differences (P less than ). In the elderly the response was not as great, values increasing from +/- to +/- ng/ml before training and from +/- to +/- ng/ml after training were recorded. These differences represented significant increases (P less than ) but did not demonstrate pre- to post-changes. Basal levels of T decreased in both groups, but were not significant. The T response to an acute bout of exercise was not significant but did increase in both age groups. In conclusion, the data presented here indicate that strength training can induce growth hormone and testosterone release, regardless of age, but that the elderly response does not equal that of the young.